CIoU protected divides (#8546)

Protected divides in IOU function to resolve https://github.com/ultralytics/yolov5/issues/8539

utils/metrics.py

@@ -225,8 +225,8 @@ def bbox_iou(box1, box2, xywh=True, GIoU=False, DIoU=False, CIoU=False, eps=1e-7
     else:  # x1, y1, x2, y2 = box1
         b1_x1, b1_y1, b1_x2, b1_y2 = box1.chunk(4, 1)
         b2_x1, b2_y1, b2_x2, b2_y2 = box2.chunk(4, 1)
-        w1, h1 = b1_x2 - b1_x1, b1_y2 - b1_y1 + eps
-        w2, h2 = b2_x2 - b2_x1, b2_y2 - b2_y1 + eps
+        w1, h1 = b1_x2 - b1_x1, b1_y2 - b1_y1
+        w2, h2 = b2_x2 - b2_x1, b2_y2 - b2_y1
 
     # Intersection area
     inter = (torch.min(b1_x2, b2_x2) - torch.max(b1_x1, b2_x1)).clamp(0) * \
@@ -244,7 +244,7 @@ def bbox_iou(box1, box2, xywh=True, GIoU=False, DIoU=False, CIoU=False, eps=1e-7
             c2 = cw ** 2 + ch ** 2 + eps  # convex diagonal squared
             rho2 = ((b2_x1 + b2_x2 - b1_x1 - b1_x2) ** 2 + (b2_y1 + b2_y2 - b1_y1 - b1_y2) ** 2) / 4  # center dist ** 2
             if CIoU:  # https://github.com/Zzh-tju/DIoU-SSD-pytorch/blob/master/utils/box/box_utils.py#L47
-                v = (4 / math.pi ** 2) * torch.pow(torch.atan(w2 / h2) - torch.atan(w1 / h1), 2)
+                v = (4 / math.pi ** 2) * torch.pow(torch.atan(w2 / (h2 + eps)) - torch.atan(w1 / (h1 + eps)), 2)
                 with torch.no_grad():
                     alpha = v / (v - iou + (1 + eps))
                 return iou - (rho2 / c2 + v * alpha)  # CIoU